Photoactivated semiconductor photocatalytic air purification

ABSTRACT

In various embodiments, an air purifier capable of destroying and deactivating airborne contaminants such as SARS-CoV-2 is described. The air purifier comprises a photocatalytic system comprising at least one photoactivated semiconductor photocatalyst and a lamp configured to irradiate and excite the at least one photoactivated semiconductor photocatalyst to generate reductive and/or oxidative reactive species from oxygen and/or water on the photocatalyst surface. In various embodiments, the photocatalytic system comprises a stack of PCB cards, each card having a photocatalytic layer disposed thereon, or a 3-dimensionally ordered macroporous (3-DOM) structure comprising an open cell lattice.

FIELD

The present disclosure generally relates to air purifiers and methods ofair purification, and in particular to air purification comprising aphotoactivated semiconductor photocatalytic system.

BACKGROUND

Air filtration commonly involves HEPA filters, activated carbon,ozonation and other oxidation processes including both ionization andphotocatalysis. However, a majority of devices and methods in this fieldphysically capture pollutants, as opposed to destroying them.

Most air purifiers and methods of air purification that involve aphotocatalyst tend to employ TiO₂, including purifiers comprising TiO₂coatings lining an enclosure radiated by UV-C light and TiO₂ catalyticmembranes comprising HEPA filters infused with TiO₂. Photocatalyticcoatings comprising TiO₂ have been marketed as having antimicrobialefficacy.

However, due to the inherent inefficiencies in air purification based onphysical capture of contaminants, or TiO₂ photocatalytic oxidationthereof, new air purifiers and methods of air purification are stillneeded. More particularly, devices and methods are needed that actuallydestroy or deactivate airborne pollutants, especially airborne microbeslike viral particles.

SUMMARY

It has now been discovered that by passing contaminated air over aphotoactivated semiconductor photocatalytic system irradiated byincident radiation, the air can be cleaned and sanitized to a greaterextent than by passing the contaminated air through filters or ionizers.It has also been discovered that air decontamination efficiency is evenfurther enhanced by channeling contaminated air through stacked layersof photoactivated semiconductor with the layers arranged such that theair flows in a serpentine pattern across each layer in series throughthe stack.

It has further been discovered that air decontamination efficiency isgreatly enhanced if each layer of photoactivated semiconductor in astacked pattern is charged with a potential to create an electric field,and an ionizer is configured to charge contaminates present in the airso that the charged particles are attracted to each layer photoactivatedsemiconductor.

In various embodiments, attraction of airborne particles, includingmicrobes, to an internal geometry of a photocatalytic system isfacilitated by both fluidic contacts and electromotive force andattraction.

It has further been discovered that air decontamination efficiency isgreatly enhanced when the decontamination process employs aphotoactivated semiconductor having a three-dimensional architecture,such as a photoactivated semiconductor having a 3-dimensionally orderedmacroporous (“3-DOM”) structure.

In various embodiments, a photoactivated semiconductor photocatalyticsystem herein comprises at least one semiconductor photocatalyst.

In various embodiments, a photoactivated semiconductor photocatalyticsystem herein comprises a single photocatalyst or a pair ofphotocatalysts, for example.

In various embodiments, a photoactivated semiconductor photocatalyticsystem herein comprises at least one semiconductor photocatalyst that iscoupled to an electron transport layer (ETL) material, coupled to a holetransport layer (HTL) material, doped or surface modified, or anycombination of the foregoing.

In various embodiments, a photoactivated semiconductor photocatalyticsystem herein is configured to produce e−/h+ pairs (i.e., electron/holepairs) upon irradiation. Initial reductive e− capture by an acceptor “A”produces reductive species such as .A⁻ radical anions, whereas initialoxidative h+ capture by a donor “D” produces oxidative species such as.D+ radical cations. The destruction of airborne pollutants, includingmicroorganisms, is catalyzed either directly by the oxidizing power ofthe photogenerated holes (h+) or the reductive power of thephotogenerated electrons (e−), or indirectly by reaction with radicals,anions, cations, .A⁻ radical anions, and/or .D+ radical cations. Some ofthe reactive species that may be formed from oxygen or water in thepresence of a photoactivated semiconductor photocatalyst include, butare not limited to, hydrogen peroxide (H₂O₂), hydroperoxyl radical(HO₂.), hydroxide anion (HO⁻), hydroperoxyl radical anion (HO₂.⁻),hydroxyl radical (HO.), hydronium ion (H₃O+) and/or superoxide radicalanion (.O₂ ⁻).

In general, a photoactivated semiconductor photocatalytic system hereinis configured to produce reductive species and/or oxidative species inthe presence of oxygen and/or water.

In various embodiments, air purifiers and methods of air purificationinclude air sanitization through the destruction/deactivation ofairborne microorganisms on the surfaces of a photoactivatedsemiconductor irradiated by incident radiation. In various embodiments,the air sanitization comprises a reduction in the number of airbornesingle-stranded RNA viral particles, including a reduction in the numberof airborne SARS-CoV-2 viral particles characterized by deactivation ofthe viral particles on the surfaces of a photoactivated semiconductorirradiated by incident radiation.

In various embodiments, an air purifier comprises a photocatalyticsystem comprising at least one photoactivated semiconductorphotocatalyst; and a lamp configured to irradiate the photoactivatedsemiconductor photocatalyst with incident radiation configured to excitethe photoactivated semiconductor photocatalyst, wherein thephotocatalyst system is configured to generate at least one reductive oroxidative reactive species in the presence of at least one of oxygen orwater in contact with the photoactivated semiconductor photocatalyst.

In various embodiments, the at least one reductive or oxidative reactivespecies comprises at least one of hydrogen peroxide (H₂O₂), hydroperoxylradical (HO₂.), hydroxide anion (HO⁻), hydroperoxyl radical anion(HO₂.⁻), hydroxyl radical (HO.), hydronium ion (H₃O+) and/or superoxideradical anion (.O₂ ⁻).

In various embodiments, the at least one photoactivated semiconductorphotocatalyst has an energy bandgap (E_(g)) of from about 12.4 eV toabout 1.24 meV, referenced to NHE.

In various embodiments, the incident radiation has an energy (E_(s)),wherein E_(s)≥E_(g) of the at least one photoactivated semiconductorphotocatalyst.

In various embodiments, the photocatalytic system comprises twophotoactivated semiconductor photocatalyst having overlapping,non-overlapping, or offset bandgaps, wherein each bandgap is from about12.4 eV to about 1.24 meV, referenced to NHE.

In various embodiments, the at least one photoactivated semiconductorphotocatalyst is modified by at least one of coupling to an electrontransport layer (ETL) material, coupling to a hole transport layer (HTL)material, doping, surface modification, or any combination thereof.

In various embodiments, the at least one photoactivated semiconductorphotocatalyst comprises an elemental material, metal chalcogenide, metaloxide, metal oxyhalide, metal phosphate, metal hydroxide, metal nitride,metal molybdate, metal vanadate, or metal tungstate, wherein the metalis Ti, C, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Tc, Ru, Rh, Pd,Ag, Cd, In, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg or Tl.

In various embodiments, the at least one photoactivated semiconductorphotocatalyst is selected from the group consisting of Bi₂Mo₃O₁₂,Bi₂Mo₂O₉, Bi₂MoO₆, BiVO₄, Bi₂WO₆, BiOBr, BiOI, MoS₂, CuO, Cu₂O, MoO₃,WO₃, BiPO₄, Ag₃PO₄, TiO₂, SnO₂, InVO₄, FeVO₄, Ag₄V₂O₇, Fe₃O₄, andmixtures thereof.

In various embodiments, the photocatalytic system comprises twophotoactivated semiconductor photocatalysts consisting of Bi₂MoO₆ andAg₃PO₄.

In various embodiments, the lamp comprises a low pressure mercury vaporlamp configured to radiate UV-C incident electromagnetic radiation at awavelength of about 254 nm.

In various embodiments, the photocatalytic system further comprises astack of PCB cards, each PBC card comprising a layer of the at least onephotoactivated semiconductor photocatalyst disposed thereon, thephotocatalytic system comprising a plurality of PCB cards stacked in aparallel and staggered arrangement creating a serpentine airflowpathway.

In various embodiments, the air purifier further comprises an ionizerconfigured to negatively or positively charge airborne contaminants inan air pathway leading into the photocatalytic system.

In various embodiments, the photocatalytic system comprises aphotoactivated semiconductor photocatalyst having a 3-DOM structure.

In various embodiments, the 3-DOM structure comprises a 3-dimensionallattice resin having an open cell structure with holes of from about 1mm to about 5 mm in average diameter, and wherein the at least onephotoactivated semiconductor photocatalyst is present in the resin or onthe resin.

In various embodiments, the 3-DOM structure comprises a 3D printed3-dimensional lattice.

In various embodiments, the air purifier further comprises a humidifierconfigured to inject water vapor into an air pathway leading into thephotocatalytic system.

In various embodiments, the air purifier further comprises an intake fanconfigured to pull contaminated air into the air purifier and move theair through the photocatalytic system.

In various embodiments, the air purifier further comprises an ozone trapconfigured to remove ozone generated from the photocatalytic system, thelamp or the combination thereof.

In various embodiments, a method of destroying or deactivating airbornecontaminants present in contaminated air comprises contacting thecontaminants present in the contaminated air with a surface of aphotoactivated semiconductor photocatalyst irradiated with incidentradiation configured to excite the photoactivated semiconductor, whereinirradiation of the photoactivated semiconductor photocatalyst generatesreductive and/or oxidative reactive species from at least one of oxygenor water present on the surface of the photoactivated semiconductorphotocatalyst and wherein the reductive and/or oxidative reactivespecies thus generated destroy or deactivate the airborne contaminants.

In various embodiments of the method, the reductive and/or oxidativereactive species generated comprise at least one of hydrogen peroxide(H₂O₂), hydroperoxyl radical (HO₂.), hydroxide anion (HO⁻), hydroperoxylradical anion (HO₂.⁻), hydroxyl radical (HO.), hydronium ion (H₃O+) orsuperoxide radical anion (.O₂ ⁻).

In various embodiments of the method, the at least one photoactivatedsemiconductor photocatalyst has an energy bandgap (E_(g)) of from about12.4 eV to about 1.24 meV, referenced to NHE.

In various embodiments of the method, irradiation of the photoactivatedsemiconductor photocatalyst further comprises irradiation with incidentradiation of having an energy (E_(s)) greater than or equal to a bandgapenergy (E_(g)) of the at least one photoactivated semiconductorphotocatalyst.

In various embodiments of the method, contacting the contaminantspresent in the contaminated air with a surface of a photoactivatedsemiconductor photocatalyst further comprises conveying the contaminatedair through a serpentine airflow pathway configured between a pluralityof spaced apart PCB cards stacked in a parallel arrangement, whereineach PCB card comprises a layer of the at least one photoactivatedsemiconductor photocatalyst.

In various embodiments, the method further comprises positively ornegatively charging the contaminants in the contaminated air prior tothe contaminants coming into contact with a surface of thephotoactivated semiconductor photocatalyst.

In various embodiments, the method further comprises applying anelectrical potential to each of the PCB cards such that anelectric/electromagnetic field produced around each PCB card attractscharged contaminants to the layer of the at least one photoactivatedsemiconductor photocatalyst.

In various embodiments of the method, destroying or deactivating thecontaminants further comprises destroying or deactivating an airbornemicroorganism.

In various embodiments of the method, destroying or deactivating thecontaminants further comprises deactivating an airborne single-strandedRNA virus particle.

In various embodiments of the method, deactivating of the airbornesingle-stranded RNA virus particle further comprises contacting theairborne single-stranded RNA virus particle with a surface of thephotoactivated semiconductor photocatalyst for a time sufficient for thereductive and/or oxidative reactive species thus generated to denature abiomolecule present in the single-stranded RNA virus particle.

In various embodiments of the method, the contaminates include airborneSARS-CoV-2 virus particles.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The subject matter is pointed out with particularity and claimeddistinctly in the concluding portion of the specification. A morecomplete understanding, however, may best be obtained by referring tothe detailed description and claims when considered in connection withthe following drawing figures:

FIG. 1 illustrates an exemplary an air purifier, in accordance withvarious embodiments;

FIG. 2 illustrates an exemplary photoactivated semiconductorphotocatalytic system further comprising a stack of PCB cards coatedwith a photoactivated semiconductor photocatalyst, wherein the PCB cardsare arranged to form a serpentine-like airflow pathway through thephotocatalytic system, in accordance with various embodiments;

FIG. 3 illustrates an exemplary single PCB card comprising a layer ofphotoactivated semiconductor photocatalyst affixed to the PCB inaccordance with various embodiments, wherein the PCB card furthercomprises electrodes for applying a potential;

FIG. 4 illustrates an exemplary photocatalytic system comprising aphotoactivated semiconductor photocatalyst having 3-DOM structure, inaccordance with various embodiments; and

FIG. 5 illustrates pressure differences as air flows through aserpentine structure consisting of stacked PCB cards configured with 12airflow channel segments, obtained in a simulation experiment. Thesimulation shows little head loss through the geometry of the cardstack.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments makes reference to theaccompanying drawings, which show exemplary embodiments by way ofillustration and their best mode. While these exemplary embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the invention, it should be understood that other embodimentsmay be realized and that logical, chemical, and mechanical changes maybe made without departing from the spirit and scope of the inventions.Thus, the detailed description is presented for purposes of illustrationonly and not of limitation. For example, unless otherwise noted, thesteps recited in any of the method or process descriptions may beexecuted in any order and are not necessarily limited to the orderpresented. Furthermore, any reference to singular includes pluralembodiments, and any reference to more than one component or step mayinclude a singular embodiment or step. Also, any reference to attached,fixed, connected or the like may include permanent, removable,temporary, partial, full and/or any other possible attachment option.Additionally, any reference to without contact (or similar phrases) mayalso include reduced contact or minimal contact.

In various embodiments, photoactivated semiconductor photocatalyticsystems are described. In various embodiments, a photoactivatedsemiconductor photocatalytic system comprises at least onephotoactivated semiconductor photocatalyst arranged in a 3-dimensionalstructure, such as, for example, a 3-dimensional structure comprisingstacks of individual layers of catalyst, or comprising a latticearchitecture.

In various embodiments, an air purifier and methods of air purificationcomprising a photoactivated semiconductor photocatalytic system aredescribed.

In various embodiments, an air purifier and associated methods of airpurification comprise a photoactivated semiconductor photocatalyticsystem further comprising at least one photoactivated semiconductorphotocatalyst and an incident light source configured to irradiate andexcite the photoactivated semiconductor photocatalyst present in thephotocatalytic system.

In various embodiments, a photoactivated semiconductor photocatalystherein is nanostructured. In various embodiments, a photoactivatedsemiconductor photocatalyst herein comprises nanoparticles. In variousembodiments, a photoactivated semiconductor photocatalyst hereincomprises a layer of nanoparticulate photocatalyst.

In various embodiments, a photoactivated semiconductor photocatalystherein is configured to produce reductive species and/or oxidativespecies upon excitation by incident radiation when at least onephotocatalyst in the photoactivated semiconductor photocatalyst is inthe presence of oxygen and/or water.

In various embodiments, a photoactivated semiconductor photocatalyticsystem herein comprises at least one semiconductor photocatalyst.

In various embodiments, a photoactivated semiconductor photocatalyticsystem herein comprises a single photocatalyst or a pair ofphotocatalysts, for example.

In various embodiments, a photoactivated semiconductor photocatalyticsystem herein comprises at least one semiconductor photocatalyst that iscoupled to an electron transport layer (ETL) material, coupled to a holetransport layer (HTL) material, doped or surface modified, or anycombination of the foregoing.

In various embodiments, a photocatalytic system further comprises astack of PCB (printed circuit board) cards, each PCB card comprising alayer of photoactivated semiconductor photocatalyst, wherein a pluralityof PCB cards are stacked so as to create a series of air channelsconnected in a serpentine-like configuration such that air must flowacross each photoactivated semiconductor photocatalyst layer present oneach PCB card in the PCB card stack.

In various embodiments, a photoactivated semiconductor photocatalyticsystem further comprises a photoactivated semiconductor photocatalysthaving a 3-dimensional structure.

In various embodiments, a photoactivated semiconductor photocatalyticsystem further comprises a photoactivated semiconductor photocatalysthaving a 3-dimensionally ordered macroporous (3-DOM) structure.

In various embodiments, an air purifier and methods of air purificationis capable of destroying/deactivating airborne pollutants, rather thansimply physically trapping the pollutants. An air purifier and methodsof air purification provide destruction/deactivation of airbornemicrobes, including the deactivation of viral particles. In variousembodiments, an air purifier and methods of air purification providedeactivation of airborne single-stranded RNA virus particles, includingdeactivation of SARS-CoV-2.

Definitions and Interpretations

As used herein, the term “photoactivated semiconductor photocatalyticsystem” refers to a catalytic system comprising at least onesemiconductor photocatalyst. In various embodiments, a photoactivatedsemiconductor photocatalytic system herein comprises a singlephotocatalyst or a pair of photocatalysts. In various embodiments, aphotoactivated semiconductor photocatalytic system herein comprises atleast one semiconductor photocatalyst that is doped, surface modified,coupled to an electron transport layer (ETL) material or coupled to ahole transport layer (HTL) material, or combinations thereof.

In various embodiments, the term “photoactivated semiconductor” refersgenerally to materials having an energy separation between their valanceband (VB) and conductance band (CB), commonly known as a “bandgap.” Thebandgap of a photoactivated semiconductor may be energetically bridgedusing thermal, electromagnetic, or photo (i.e., light-based) energy.When activated by a sufficiently large energy source having energy(E_(s)) greater than or equal to the energy bandgap (E_(s)≥E_(g)),electrons to migrate to the CB, leaving behind holes in the VB (i.e.,forming e−/h+ pairs). After the creation of a e−/h+ pair, the electroncan either drop back down from the conductance band filling the hole inthe valance band in what is called recombination, or the holes andelectrons can be separated so the holes and electrons may participate inoxidation and reduction reactions respectively. In various embodimentsherein, a photocatalyst is a light activated semiconductor which isactivated with the aim of facilitating reduction and/or oxidationreactions. The redox reactions serve the purpose of purifying air whichmay be achieved via direct photocatalyst/pollutant interaction or apollutant's interaction with one of the photocatalyst's reactiveproducts, byproducts or intermediate products, such as e.g., neutralradicals, anions, cations, radical anions, and/or radical cations,including, but not limited to, hydrogen peroxide (H₂O₂), hydroperoxylradical (HO₂.), hydroxide anion (HO⁻), hydroperoxyl radical anion(HO₂.⁻), hydroxyl radical (HO.), hydronium ion (H₃O+) and/or superoxideradical anion (.O₂ ⁻)). The composition of a semiconductor is a largechemical family containing single element specimens (e.g., Si),inorganic compounds (e.g., TiO₂), organic compounds (e.g., C₁₈H₁₂), andcombination organic-inorganic compounds (e.g., CH₃NH₃PbI₃ also known asmethylamino-PbI₃ or “MAPbI₃”). These substances may occur or be preparedin various physical forms including, but not limited to, crystalline,amorphous, polymeric, or combinations thereof.

Generally, semiconductor photocatalysts for use herein can becategorized by their chemical nature and/or their physicalcharacteristics.

In various embodiments, a semiconductor for use herein is selected fromthe group of chemical substances consisting of single elementalmaterials, metal chalcogenides, metal oxides, metal oxyhalides, metalphosphates, metal hydroxides, metal nitrides, metal molybdates, metalvanadates, metal tungstates, and mixtures thereof, wherein the metalcomprises any metal falling within the block of elements comprisingPeriods 4, 5 or 6 and Groups 4-13 elements of the Periodic Table of theElements. The metals encompassed within this block of the Periodic Tableare Ti, C, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Tc, Ru, Rh, Pd,Ag, Cd, In, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg and Tl. Exemplarysemiconductor photocatalysts for use herein include, but are not limitedto, Bi₂Mo₃O₁₂, Bi₂Mo₂O₉, Bi₂MoO₆, BiVO₄, Bi₂WO₆, BiOBr, BiOI, MoS₂, CuO,Cu₂O, MoO₃, WO₃, BiPO₄, Ag₃PO₄, TiO₂, SnO₂, InVO₄, FeVO₄, Ag₄V₂O₇,Fe₃O₄, and mixtures thereof.

In various embodiments, a semiconductor photocatalyst may be chemicallymodified. To increase the effectiveness of a photocatalyticsemiconductor there are several methods of optimization: (1) therecombination rate of e−/h+ pairs can be lowered so there are more holesand electrons available to react; (2) reduction and oxidation reactionsmay be physically distanced to eliminate competitive redox reactions;(3) the bandgap may be tuned to utilize incident light more efficiently;(4) semiconductors may be placed in contact to create various junctions,or the surface may be modified to increase the adsorption, absorption,chemisorption or otherwise contact with pollutants to increaseperiodicity of reactions. These are the aims of the various types ofmodification. To achieve any one or combination of these modifications,a semiconductor photocatalyst herein may be modified by at least one ofcoupling to an electron transport layer (ETL) material, coupling to ahole transport layer (HTL) material, doping, surface modification, orany combination thereof.

In various embodiments, semiconductor photocatalysts for use herein maybe modified or further optimized in methods which include, but are notlimited to, metal and non-metal doping, surface alkalization, surfaceloading of metal and/or carbon, attachment to an electron transportlayer (ETL), attachment to a hole transport layer (HTL), adjustment ofparticle size and/or geometry, or placing a semiconductor photocatalystin contact with another semiconductor to form a junction (e.g.,homojunction, heterojunction, etc.).

As used herein, the terms “electron transport layer” (ETL) and “holetransport layer” (HTL) refer to substances capable of reducing therecombination of e−/h+ pairs, e.g. altering the rate of recombinationsuch that the substances undergoing redox reactions, namely oxygenand/or water, have certain time to react with the photogeneratedelectrons (A→A⁻) and photogenerated holes (D→D+). In variousembodiments, an ETL or HTL material for use herein is selected from thegroup consisting of single chemical elements such as metals, metalchalcogenides, metal oxides, metal oxyhalides, metal phosphates, metalhydroxides, metal nitrides, metal molybdates, metal vanadates, metaltungstates, and mixtures thereof, wherein the metal comprises any metalfalling within the block of elements comprising Periods 4, 5 or 6 andGroups 4-13 elements of the Periodic Table of the Elements. The metalsencompassed within this block of the Periodic Table are Ti, C, Cr, Mn,Fe, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Hf, Ta,W, Re, Os, Ir, Pt, Au, Hg and Tl. In various embodiments, an ETL or HTLmaterial may also comprise a metal carbonate, or a composite of one ofthe above-mentioned chemical species and a metal carbonate, or grapheneoxide, or an organic polymer, typically a fluorinated block or di-blockelectron conducting copolymer (e.g., a polythiophene). In variousnon-limiting embodiments, an ETL or HTL material for use herein is ametal oxide, or a composite of a metal oxide and a metal carbonate. Invarious embodiments, an ETL or HTL may comprise carbon, such as in theform of graphene, or a carbon nanotube (CNT, SWCNT, etc.). In variousembodiments, an ETL or HTL material is selected from the groupconsisting of a metal M, ZnO, TiO₂, SnO₂, Nb₂O₅, MoO₃, WO₃, V₂O₅, NiO,Cs₂CO₃, graphene, graphene oxide, CNT, SWCNT, and combinations thereof.

The term “dopant” takes on its ordinary meaning in inorganic chemistry.A photoactivated semiconductor photocatalyst herein may be “doped.”Dopants for use herein include, but are not limited to, Eu(III), F,Nd(III), Ag(I), Gd(III), Nb(V), Fe(III), Sm(III), Yb(III), Er(III),Cu(II), B, N, PO₄ ³⁻, Co(II), Ni(II), and combination thereof. So, forexample, a BiVO₄ photoactivated semiconductor photocatalyst for useherein may be doped with 0.01 wt. % Ag(I) powder. More extensive listsof dopants usable herein, including both organic and inorganic dopants,may be found in the semiconductor literature.

In various embodiments, a semiconductor photocatalyst for use herein inchosen on the basis of the photocatalyst exhibiting certain physicalcharacteristics. For more than one semiconductor photocatalyst in aphotoactivated semiconductor photocatalytic system, any twosemiconductor photocatalysts may be chosen on the basis of variousphysical properties that they share, or that relate in some way.

In various embodiments, a semiconductor photocatalyst for use herein hasa bandgap of from about 12.4 eV to about 1.24 meV. In embodiments wheretwo semiconductor photocatalysts are present, their individual bandgapsmay be overlapping, non-overlapping, or offset, as explained below.

When at least two semiconductor photocatalysts are present in a systemherein, the bandgaps must be compared. A bandgap is the differencebetween the VBM valance band maximum and the CBM conductance bandminimum. With these two energy levels dependent on electron shellstructures and bond dynamics, it is possible to see a bandgap of thesame size appearing at different locations; occurring when twosubstances have different VBM values but the same spacing between VBMand CBM. A bandgap overlap occurs when the bandgaps of two substances atleast partially cover the same energies (e.g., substance 1 has a VBM of1 eV and a bandgap of 2 eV and substance 2 has a VBM of 2 eV and abandgap of 0.5 eV). Therefore, two substances with a 1 eV bandgap mayhave overlapping, non-overlapping (i.e., no junction), or offsetbandgaps. If two substances have the same VBM and bandgap they create ahomojunction. In most cases though there is an offset whichcharacterizes a heterojunction. All junctions overlap, but not alloverlaps are offset. The size and degree of offset further categorizeheterojunctions. For example, two substances with the same bandgap andslightly different VBM form what is called a type-H hetero junction,while two substances with the same bandgap, but the VBM of one slightlybelow the CBM of the other, form a z-scheme heterojunction.

In various embodiments, semiconductor photocatalysts herein are capableof generating reductive and/or oxidative reactive species in thepresence of oxygen and/or water. Semiconductor photocatalysts for useherein are chosen for their ability to generate at least one of hydrogenperoxide (H₂O₂), hydroperoxyl radical (HO₂.), hydroxide anion (HO⁻),hydroperoxyl radical anion (HO₂.⁻), hydroxyl radical (HO.), hydroniumion (H₃O+) and/or superoxide radical anion (.O₂ ⁻) in the presence of atleast one of oxygen or water.

In various embodiments herein, semiconductor photocatalysts are chosenin consideration of the incident radiation energy required for theirexcitation. As a general rule, the following approximations apply:

Infrared Range: 0.00124 meV-1.65 eV, or 1 nm to 750 nm;

Visible Range: 1.65 eV-3.1 eV, or 750 nm to 400 nm: and

Ultraviolet Range: 3.1 eV-12.4 eV, or 400 nm to 100 nm.

As used herein, the term “3-DOM” refers to “3-dimensionally orderedmacroporous” structure, which is a type of three-dimensionalarchitecture on a macroscopic scale. Self-assembling versions of 3-DOMstructures are sometimes referred to as “inverse opal.” Herein, aphotoactivated semiconductor photocatalytic system may comprise a 3-DOMstructure. In various embodiments, this three-dimensionally orderedporous material dictates the interaction of incident photos on thephotocatalyst within the matrix, and creates certain airflow pathwaysand interactions between airborne pollutants and photocatalyst surfaces.In various embodiments, 3-DOM structure is used to create athree-dimensional macro-structured photocatalytic system from aphotoactivated semiconductor photocatalyst. In various embodiments, aphotocatalytic system comprises a 3-DOM photoactivated semiconductorphotocatalyst.

In various embodiments, a 3-DOM structure can be made by 3D printing aninverse opal structure on a millimeter scale described using SLA or SLS3D printing techniques with a photocatalytic resin (either infused or atype of sol-gel), or metal sintering material, respectively. 3-DOMmaterials include, but are not limited to, PFA*, FEP*, PTFE*, PVDF*,aluminum, HDPE, LDPE, fiberglass, quartz/fused quartz*, copper, and gold(*—indicates transparent materials). As discussed further below, aphotoactivated semiconductor photocatalytic system having a 3-DOMstructure may feature a photocatalytic resin lattice matrix, one or morephotocatalysts embedded within a non-photoactive resin lattice matrix,one or more photocatalysts on or in the lattice, such as on the surfacesof the open cell structure, or any combination of the above. Ininstances where there are more than one photocatalysts present in asystem, they can be distributed in any way in the 3-DOM structure (e.g.,one catalyst is the resin, or one catalyst is in the resin and anotheron the lattice, and so forth).

As used herein, the terms “ultraviolet light” and “ultravioletradiation” interchangeably refer to that portion of the electromagneticspectrum from about 100 to about 400 nm in wavelength, corresponding to12.4 eV to 3.1 eV. Although UV light may be used as the incidentradiation for some of the types of photocatalysts chosen for use herein,any wavelength or range of wavelengths, including visible light, may beused in conjunction with the photocatalysts herein, depending on thenature of the photocatalyst. In various embodiments, an incidentwavelength may be chosen for its dual function, namely, to activate aparticular semiconductor photocatalyst and inactivate microorganisms. Anexample is UV-C incident light at about 250 nm, known to activatecertain photocatalytic systems and denature microorganisms such asSARS-CoV-2 virus.

As used herein, the term “lamp” is used broadly to include any lightenergy source, regardless of whether the source resembles a traditionalincandescent bulb or not. Non-limiting examples of lamps include mercuryvapor lamps, halogen lights, light-emitting diodes (LEDs, including UVLEDs and plasma UV emitters), gas discharge lamps, electrical arcs,black lights, fluorescent lamps, incandescent lamps, lasers, and plasmaand synchrotron sources.

As used herein, the term “single-stranded RNA virus” takes on itsordinary meaning in virology to include both positive-sense RNA viruses(Group IV) and negative-sense RNA viruses (Group V). The Group IVviruses include such well-known pathogens as hepatitis C, West Nile,dengue, MERS, and SARS, including SARS-CoV-2. The Group V viruses alsoinclude well-known pathogens, the most infamous perhaps being Ebola. Forsimplicity, the terms “Groups IV/V viruses” or “ssRNA viruses” may beused interchangeably with one another and interchangeably with the termfully written out terms “positive-sense single-stranded RNA viruses” and“negative-sense single-stranded viruses.”

As used herein, the terms “air sanitization,” “sanitizing air,” and“sanitized air,” are interchangeably used to indicate at least somelevel of microbe kill (i.e., a measurable reduction in the number ofairborne microorganisms) by an air purifier or methods of airpurification according to the present disclosure. For example, air thatis sanitized may indicate a sanitizing level (3-log, or 99.9%) reductionin at least one organism. Microbes, or microorganisms adversely effectedby an air purifier or methods of air purification disclosed herein, mayinclude any species of bacteria, virus, mold, yeast, or spore. Thus, airsanitization encompasses reduction of airborne bacteria, viruses, molds,yeasts, or spores. In various embodiments herein, an air purifier ormethods of air purification herein, reduce the number of airborne viralparticles, including single-stranded RNA viruses such as SArS-CoV-2.

In various embodiments, airborne microorganisms coming into contact witha photoactivated semiconductor photocatalyst system herein,appropriately irradiated with incident energy light, experience celldeath, destruction, and/or inactivation. The sanitizing effect madepossible by the photocatalyst system is not limited by a particularmechanism of action, although it remains possible that reductive and/oroxidative reactive species generated from oxygen and/or water present onthe photocatalyst are involved. For example, an air sanitizing effectmeasured for a photocatalyst system may be the result of intracellularmutations, inhibition of certain cellular processes, rupture of a cellwall, or a nondescript inactivation of the organism, such as in the caseof viruses that may be deactivated simply by free-radical breakdown ofbiomacromolecules such as RNA present in the viruses. An example ofinactivation of the SARS-CoV virus on a titanium photocatalyst has beendescribed in Wei Han, et al., “The inactivation effect of photocatalytictitanium apatite filter on SARS virus,” Progress in Biochemistry andBiophysics, 31(11), 2004.

I. Air Purifier—General Aspects

In various embodiments, an air purifier is described. The air purifieris capable of destroying/deactivating airborne pollutants, including theability to reduce the number of viable airborne microbes in contaminatedair, including bacteria, viruses, molds, yeasts and spores. A measurablereduction in the number of airborne microbes is associated withdeactivation of the organisms rather than physical entrapment where themicrobes might still be viable even though they are physicallyimmobilized. Here, reductive and/or oxidative reactive species producedfrom the photoactivated semiconductor photocatalytic system uponexcitation, deactivate microorganisms in contact with the surfaces ofthe photoactivated semiconductor photocatalyst, such as throughdenaturing of biomolecules essential to the organism.

In various embodiments, an air purifier comprises a photocatalyticsystem and an incident light source configured for the photocatalyticsystem. The photocatalytic system further comprises a photoactivatedsemiconductor. The incident light source is configured and isappropriately positioned so as to excite the photoactivatedsemiconductor within the photocatalytic system. In various embodiments,the photocatalyst system is configured to generate reductive and/oroxidative reactive species from oxygen or water. In various embodiments,the photocatalytic system is configured to generate at least one ofhydrogen peroxide (H₂O₂), hydroperoxyl radical (HO₂.), hydroxide anion(HO⁻), hydroperoxyl radical anion (HO₂.⁻), hydroxyl radical (HO.),hydronium ion (H₃O+) and/or superoxide radical anion (.O₂ ⁻) by thechoice of the photoactivated semiconductor photocatalyst and thepresence of at least one of oxygen or water.

In various embodiments, a photoactivated semiconductor photocatalyst isdisposed as a layer on a printed circuit board (PCB) referred to hereinas a “PCB card.” In various embodiments, a photoactivated semiconductorphotocatalyst is adsorbed onto the card and cured thereon to produce thePCB card comprising the photoactivated semiconductor photocatalyst. Invarious embodiments, the adhesive may be applied to a PCB card bydipping, brushing, rolling, spraying, amongst other methods. Particlesof semiconductor photocatalyst may then be adhered to the surface of thePCB card via the adhesive present. In various embodiments, thephotocatalyst may be premixed with an adhesive and the mixture appliedto the PCB card by any of the aforementioned methods.

In various embodiments, a photocatalyst is dispersed on an adhesivecoated PCB card by dusting, fogging, sprinkling, sieving, dipping,dabbing, etc. After the photocatalyst is dispersed, the adhesive can becured according to the nature of the adhesive used. The specificcombination of application methods depend on geometry of the PCB cardand the overall photocatalytic system. In other variations, particles ofphotocatalyst may be hot-pressed into an appropriate surface. This canbe done by heating for example PVDF and pressing it into a glass platewith photocatalyst particles dusted onto its surface and then repeatingthe process for both sides. As an alternate, a photocatalyst may besynthesized directly on the surface of a photocatalytic system or anelement therein using normal methods such as vapor deposition,spin-coating, sol-gel, epitaxy molecular beams, etc. These synthesestend to be more demanding and expensive but have greater rigor andcontrol.

In various embodiments, a stack of these coated PCB cards areappropriately arranged to destroy/deactivate airborne pollutantsconveyed past the photoactivated semiconductor photocatalyst layers onthe PCB cards. In various embodiments, an electrical potential isapplied across each PCB card such that the photoactivated semiconductorphotocatalyst present on the PCB card is, in effect, polarized. Theapplied potential to the PCB card results in an electric/electromagneticfield around the PCB card. In various embodiments, an ionizer isprovided upstream from the stack of PCB cards to electrically chargepollutants present in the contaminated air so that the charged particlescollect on the photoactivated semiconductor photocatalyst layers byelectromotive forces. In various embodiments, the polarized PCB cardsreplace the collector plates in a conventional ionizer. In alllikelihood, the photocatalytic layer itself is not polarized per se, butrather the underlying electrodes are polarized by the applied potentialsuch that charged pollutant particles run into the photocatalyst layerthat blocks the route of the charged particles to the polarizedelectrodes underneath the photocatalyst layer.

In various embodiments, the photocatalytic system further comprises aphotoactivated semiconductor photocatalyst coated onto and into athree-dimensional lattice, such as a 3-DOM structure. In variousembodiments, the photoactivated semiconductor photocatalyst is thelattice, or is within the lattice.

In various embodiments, and in addition to at least one photocatalyticsystem and associated incident radiation source, an air purifier hereinmay further comprise any one or combination of an exterior housing, anair intake port, a prefilter, an intake fan to push air through, anionizer, air splitters, air collimators, and capillary channels asneeded, air ducting, an ozone trap, an outlet fan to pull air through,an outlet port, a power supply, an external power supply cord, variousindicator lights, circuit boards, computer processors and controllers,sensors, internal wiring, bus bars, transformers, rectifiers, alarms,and remote controls as needed. Some of these general aspects will beappreciated in reference to the various drawing figures.

With reference now to FIG. 1, an air purifier 100 in accordance withvarious embodiments comprises at least one photocatalytic system (twoare shown, 140 a/140 b, which may be the same or different) and at leastone lamp 115 physically configured and appropriately positioned toirradiate the photocatalytic system 140 with incident radiation 118. InFIG. 1, the bolded and dashed directional arrows such as 112 and 114indicate directional air flows. The lighter dashed directional arrows118 indicate electromagnetic radiation, such as IR, UV or visible light,emanating from the lamp 115. The left side of the air purifier 100 asillustrated is the intake side for entry of contaminated air to bepurified, whereas the right side of the air purifier 100 as illustratedis the outlet side for exit of the purified air.

In FIG. 1, two separate photocatalytic systems 140 a and 140 b areconfigured on opposite sides of the lamp 115, although this particularconfiguration is not meant to be limiting. Any number of photocatalyticsystems can be employed in the air purifier 100. For example, aplurality of photocatalytic systems (140 a, 140 b, 140 c, and so forth)can be configured around the lamp 115 with the lamp 115 centrallypositioned to irradiate the multiple photocatalytic systems positionedradially around the lamp 115. In other embodiments, more than one lamp115 (115 a, 115 b, 115 c, and so forth) may be utilized to irradiatemultiple photocatalytic systems, and the various lamps may be physicallyconfigured to irradiate the same, different or overlapping wavelengthsas needed. For example, one lamp may irradiate UV-C light at 254 nm toexcite a particular photocatalytic system, whereas another lamp presentin the air purifier 100 may irradiate light in the visible spectrum toexcite another photocatalytic system. In various embodiments, aplurality of LEDs may be configured around or within a photocatalyticsystem. In various embodiments, the photocatalytic systems may bedifferent, (e.g., photocatalytic systems 140 a and 140 b), in that eachmay have a unique photoactivated semiconductor photocatalystconfiguration, or a unique physical structure, requiring its owndedicated lamp 115 capable of irradiating a particular wavelength ofincident radiation appropriate for that particular photocatalyticsystem. For example, one photocatalytic system 140 a may require UV-C(254 nm) incident radiation to excite the photoactivated semiconductorphotocatalyst therein, whereas another photocatalytic system 140 b mayrequire visible light to excite the photoactivated semiconductorphotocatalyst therein. In various embodiments, optical fibers may beused to convey light through convoluted pathways and into narrowinterstices present in the photocatalytic system that might otherwisenot receive incident radiation from the lamp 115.

As will be described in more detail herein, each photocatalytic system140 a/140 b comprises a photoactivated semiconductor photocatalystconfigured in a three-dimensional architecture. In various embodiments,the photocatalytic system may comprise a three-dimensional array ofstacked PCB cards, wherein each PCB card comprises a layer of thephotoactivated semiconductor photocatalyst. In other embodiments, thephotocatalytic system may comprise a three-dimensional lattice, such asa 3-DOM structure, having the photoactivated semiconductor photocatalyston and/or in the lattice, or where the lattice matrix material is aphotocatalyst. In various embodiments, the photocatalytic systemcomprises a 3-DOM photoactivated semiconductor photocatalyst.

In various embodiments, the lamp 115 provides incident radiation ofenergy (E_(s)) greater than or equal to the energy bandgap (E_(g)) ofeach of the photoactivated semiconductor components that may be presentwithin the photocatalytic system. That is, the lamp is configured suchthat E_(s)≥E_(g) for at least one photocatalyst in the system. Invarious embodiments, the lamp 115 comprises a lamp that providesinfrared light. In various embodiments, the lamp 115 comprises a lampthat provides visible light. In various embodiments, the lamp 115comprises a UV lamp. In various embodiments, the lamp 115 comprises aUV-C lamp providing incident UV radiation 118 at from about 200 nm toabout 280 nm. In various embodiments, the UV-C lamp is configured toprovide incident radiation 118 having a wavelength of about 254 nm. Incertain embodiments, the lamp 115 comprises a mercury low pressure UVlamp, further comprising a quartz tube, an electrode, mercury and aninert gas. An exemplary low pressure lamp emitting almost entirely 254nm radiation is available, for example, from Helios Quartz America, Inc,Sylvania, Ohio.

In various embodiments, the air purifier 100 may further comprise ahousing 110 with panels defining an exterior surface and an interiorspace. The housing may be constructed of conventional materials, such asplastic or metal, and may appear simply as a galvanized sheet metal box.The housing 110 may be designed for aesthetics if the air purifier 100will be visible to the user, such as if configured as a portableappliance, or the housing 110 might be entirely utilitarian where theoutward appearance may not be that important, such as if the airpurifier 100 is configured for retrofitting into an existing HVACsystem. The housing may have any shape or size, and may be rectangularin cross-section as illustrated in FIG. 1. The housing 110 may includeany number of vents and cooling fans to move heat from the interior ofthe air purifier (e.g., heat generated from the lamps), any number ofhinging, sliding or otherwise removable access doors or panels,indicator lights such as LEDs, switches, buttons, piezo beepers/buzzers,Bluetooth transmitter, water inlet/outlet fittings, and electricalcords. Any one or combination of these elements may be physicallymounted on or through the housing 110 and may be configured to bepurposely visible on or audible from the exterior surface of the housing110. These features are not illustrated in FIG. 1 for the sake ofclarity.

In various embodiments, the air purifier 110 may include any number andtype of sensors (e.g., 180 a, 180 b, etc.), along with a microprocessorto adjust and/or maintain heating, cooling, pressure, humidity, airflow,etc., based on the data collected for these variables. In variousembodiments, the air purifier 110 may further comprise at least onesensor 180 a/180 b selected from chemical sensors (VOCs, ozone, etc.),temperature sensors, pressure sensors, humidity/moisture sensors, andairflow/air speed sensors.

In various embodiments, the one or more sensors 180 a/180 b may beplaced both before and after a photocatalytic system (140 a/140 b),respectively, to measure variables such as total VOCs (TVOCs), pressure,temperature, air speed, humidity, ozone content, etc., on both sides ofa photocatalytic system. These two data points, a data point obtainedfrom sensor 180 a configured in an inlet to the photocatalytic system140 a, and a data point obtained from sensor 180 b configured in anoutlet from the photocatalytic system 140 a, may then be relayed to amicrocontroller/microprocessor configured to perform operations such asincreasing/decreasing lamp power (incident radiation intensity), airhumidifying, fan speeds, and the like, with the goal of maintaining highefficiency VOC-input VOC-output ratio, indicative of clean air. Thisgives the purifier a way to ensure a predetermined single pass air scrublevel utilizing real-time internal data, and serves to conserve energyin cleaned spaces by dropping system power demands when pollutant levelsare measurably low. The microcontroller may be external to the airpurifier 110, and may comprise a laptop computer or other device. Thesensors 180 a/180 b may communicate wirelessly to a computer.

With continued reference to FIG. 1, the air purifier 110 furtherincludes air ductwork. This ductwork may be as simple as necessary toconvey contaminated intake air through the one or more photocatalyticsystems and back out to an environment outside of the air purifier 100.The ductwork internal to the air purifier 100 may also be as complicatedas needed to convey air into and through a multiplicity ofphotocatalytic systems, each one possibly comprising its own air flowlabyrinth, and through any number of other elements in the device suchas filters, ionizers, and sensors. So, for example, intake air 112 maycome into an intake tube 122 that splits into similar or identical airchannels 124 a and 124 b. In this example, there are two air channels124 a and 124 b in order to coincide with use of two photocatalyticsystems 140 a and 140 b. As mentioned above, an air purifier 100 maycomprise a plurality of individual photocatalytic systems, and thus theair ductwork may be much more complicated than illustrated in FIG. 1.Air may need to be split into a plurality of air channels (124 a, 124 b,and so forth) so as to feed contaminated intake air into each one of aplurality of photocatalytic systems (140 a, 140 b, and so forth). Asfurther illustrated in FIG. 1, air that has been purified by thephotocatalytic systems 140 a/140 b is then conveyed through outlet airchannels 126 a and 126 b and into an outlet tube 128. As mentioned, whenmore than two photocatalytic systems are employed, the number of outletair channels (126 a, 126 b, and so forth) can match the number of intakeair channels (124 a, 124 b, and so forth), and match the number ofphotocatalytic systems employed (140 a, 140 b, and so forth). Purifiedair 114 then exits the air purifier 100 through the outlet port 118.Features at the intake side and the outlet side of the air purifier 100are discussed in more detail herein. Although the air purifier isillustrated in FIG. 1 with only one intake fan 120, any number of fansmay be employed in the air ductwork. In other words, a single fan 120 atthe intake end of the device may be insufficient to push air through andout of the air purifier 100. Additional fans may be configured withinair channels on either or both the intake and outlet side of the device.Further, an outlet fan may be employed to pull air 114 out of the airpurifier. All of the fans may be controlled by a computer processor,each one being adjusted so that the air flow through the entire airpurifier 100, and the purification of contaminated air, are optimized.

In various embodiments, the air purifier 100 comprises at least oneionizer 170 a/170 b configured in the air ductwork on the inlet side ofthe air purifier 100. In the embodiments illustrated, a first ionizer170 a is configured in the intake air channel 124 a and a second ionizer170 b is configured in the intake air channel 124 b. Each of the one ormore ionizers are configured to provide a charge on various airbornepollutants present in the contaminated air prior to entry of thecontaminated air into the one or more photocatalytic systems 140 a/140b. As explained in more detail herein, various elements of aphotocatalytic system herein can act as the collection plates in aconventional ionizer, such that the charged pollutant particles enteringthe photocatalytic system 140 a/140 b are attracted to various chargedfeatures within the photocatalytic system 140 a/140 b, such as layers ofphotoactivated semiconductor photocatalyst. In various embodiments, theat least one ionizer 170 a/170 b is configured to positively chargepollutant particles or negatively charge pollutant particles. In variousembodiments, the at least one ionizer 170 a/170 b is configured topositively or negatively charge airborne microorganisms, such as virusparticles, before the microorganisms enter the one or morephotocatalytic systems 140 a/140 b where they are attracted to layers ofphotoactivated semiconductor photocatalyst having a charge.

In various embodiments, the ionizer 170 a/170 b may comprise anelectrostatic discharge ionizer (ESD) configured to provide coronaionization into the contaminated air passing therethrough. In variousembodiments, the ionizer may comprise ESD needles protruding into theairduct, as illustrated in FIG. 1. In various embodiments, an electricalcurrent creates bipolar ionized air. The ionizer applies a high-voltageelectrical current composed of a flow of electrons to the protrudingneedles Electrostatic repulsion causes the electrons to detach from theneedles where they attach themselves to the pollutants in thecontaminated air, forming negative ions, which are attracted to thevarious electrically charged elements within the photocatalytic systems140 a/140 b. Corona ionization may comprise AC and DC ionization. ACionization uses one emitter to produce both positive and negative ions,whereas DC ionization uses separate positive and negative emittersrunning simultaneously to create bipolar ions. In various embodiments,the negative pole of the ionizer may be connected to the ESD needles andthe positive pole of the ionizer connected to a feature within thephotocatalytic system. In other embodiments, the ionizer ESD needlesprovide bipolar ions that attach to various features in thephotocatalytic system that are similarly bipolarized with both (+) and(−) poles.

In various embodiments, the air purifier 100 comprises at least onepower supply 160 and its associated components such as step-downtransformers, AC-DC rectifiers, wiring and connectors. The power supply160 may be wired at least to the intake fan 120 via the wiring 162, tothe lamp 115 via the wiring 164, and to the ionizers 170 a/170 b (wiringnot shown) so that the required electrical power (voltage, phase,current) is supplied to these and other electrical components present,such as additional fans, sensors, and so forth. More than one powersupply 160 can be employed, such as having a high voltage/amperage powersupply for the one or more lamps, and a low voltage/amperage powersupply for such components as fans and circuit boards, or such that ACis supplied to one component and DC to another. One or more externalelectrical supply cords can be wired to the power supply, such asthrough a grommet configured in the air purifier housing 110, with theend of the cord having the appropriate configuration for 110V or 220Vand ground, or the necessary pins for electrical outlets found in othercountries besides the U.S.

In various embodiments, the air purifier 100 may further comprise aprefilter 130 as illustrated in FIG. 1. A prefilter for use herein maybe configured on either side of the intake fan 120 so long as theprefilter 130 is positioned before the photocatalytic systems 140 a/140b. The purpose of the prefilter 130 is to remove large particulates,particularly inanimate materials, from the intake air that wouldotherwise accumulate on the photocatalytic system and eventually blockthe photocatalytic surfaces.

In various embodiments, the prefilter 130 comprises a HEPA filter, whichmay be any grade of air filter. HEPA filters are generally categorizedby MERV ratings (Minimum Efficiency Reporting Value) ranging from 1 to20. For use herein, the prefilter 130 may comprise a filter having aMERV rating of up to about 12. Filters with MERV ratings from about14-16 are capable of trapping airborne bacteria, and filters with MERVratings from about 17 up to 20 are capable of trapping airborne viruses.Filtration at these levels is not necessary since it is thephotocatalytic systems in the air purifier 100 that will destroy theairborne bacteria, viruses, molds, yeasts and spores. The prefilter 130may be chosen for its ability to filter out the larger inanimateparticles coming into the air purifier 100 such that the photocatalyticsystems 140 a/140 b are not soiled and rendered ineffective by a buildupof these soils. For example, the prefilter 130 may comprise a home orinstitutional air filter having a MERV rating of from 1 to about 12, andmore preferably from about 5 to about 12. The prefilter 130 may comprisea cheap disposable filter, a better quality home box filter, or asuperior quality commercial HVAC filter. The prefilter 130 may beappropriately sized to cover the intake port 116, and may be fit insidethe intake port 116. In various embodiments, the intake port 116 and theprefilter 130 form an assembly configured to be removable from thehousing 110 so that the prefilter 130 can be easily replaced whenneeded.

With continued reference to FIG. 1, the air purifier 100 may comprise anozone trap 150 configured on the outlet end of the air purifier 100. Forexample, the ozone trap may be inline within the outlet tube 128, orjust before or after the outlet tube 128. In various configurations, theozone trap 150 may be positioned at the end of the outlet side of theair purifier, such as between the outlet tube 128 and the outlet port118. In this way, the purified air 114 exiting from the outlet port 118of the air purifier 100 is stripped of any ozone that may have formedfrom oxidative processes in the photocatalytic systems 140 a/140 b andfrom the lamp 115 or from any ionizer that may be present.

In various embodiments, the ozone trap 150 may be any sort of filter orsupport impregnated with one or more substances, like activated carbon,permanganate, perlite or other ozone destroyer. In various embodiments,the ozone trap 150 comprises a manganese dioxide/copper oxide catalyst.This ozone trapping catalyst is available under the brand name Carulite®200, from Carus Corporation, LaSalle, Ill.

Photocatalytic Systems

As discussed herein, an air purifier and methods of air purification inaccordance with the present disclosure comprise at least onephotocatalytic system 140 a/140 b, such as shown in FIG. 1 (illustratedwith two photocatalytic systems 140 a and 140 b that may be the same ordifferent). In various embodiments, a photocatalytic system for useherein comprises at least one photoactivated semiconductorphotocatalyst.

In various embodiments, the photocatalytic system comprisesphotoactivated semiconductor photocatalyst nanoparticles. In instanceswhere the photoactivated semiconductor photocatalyst comprises more thanone substance (e.g., a pair of photocatalysts, or a semiconductorphotocatalyst coupled to an ETL or HTL material), each component may beintermixed within a single nanoparticle, e.g., with a core/shellstructure, or each component may consist of its own nanoparticles andthese nanoparticles of different composition are intimately mixed. Invarious embodiments, photoactivated semiconductor substances arecrystalline or amorphous and not comprising identifiable nanoparticles.

In various embodiments, the photocatalytic system comprises athree-dimensional structure. A three-dimensional overall structure of aphotocatalytic system may be the result of coating a photoactivatedsemiconductor photocatalyst onto and into a macroscopically sizedthree-dimensional lattice, such a 3-DOM structure, or may be the resultof stacking coated PCBs into a 3-dimensional array, wherein each PCBcard comprises a layer of a photoactivated semiconductor photocatalyst.In either of these two non-limiting embodiments, a three-dimensionalconfiguration (3-DOM structure or stacked coated PCB cards) providesunique airflow passageways for a photocatalytic system, thus increasingthe likelihood that airborne pollutants will interact with thephotoactivated semiconductor photocatalyst. These and other embodimentsare discussed in more detail herein.

In various embodiments, a photoactivated semiconductor photocatalyst foruse in the photocatalytic systems herein comprises at least onesemiconductor photocatalyst as defined herein above. In variousembodiments, two photoactivated semiconductor photocatalysts for use inthe photocatalytic systems herein are independently selected from thegroup consisting of Bi₂Mo₃O₁₂, Bi₂Mo₂O₉, Bi₂MoO₆, BiVO₄, Bi₂WO₆, BiOBr,BiOI, MoS₂, CuO, Cu₂O, MoO₃, WO₃, BiPO₄, Ag₃PO₄, TiO₂, SnO₂, InVO₄,FeVO₄, Ag₄V₂O₇, Fe₃O₄, and mixtures thereof.

In various embodiments, a photoactivated semiconductor photocatalyticsystem comprises at least two semiconductor photocatalysts. In variousembodiments, a photoactivated semiconductor photocatalytic systemcomprises a mixture of Bi₂MoO₆ and Ag₃PO₄. In various embodiments, aphotoactivated semiconductor photocatalytic system comprises a mixtureof Bi₂MoO₆ and Ag₃PO₄ in a (w/w) ratio of from about 1:5 to about 1:15.In various embodiments, a photoactivated semiconductor photocatalyticsystem comprises a mixture of Bi₂MoO₆ and Ag₃PO₄ in a (w/w) ratio ofabout 1:9.

Formation of reductive and/or oxidative reactive species as discussedherein above requires oxygen or water molecules on the photoactivatedsemiconductor photocatalyst. Oxygen will always be present in thecontaminated air entering the air purifiers disclosed herein forpurification.

For the air purifier and methods of air purification herein, it maysuffice that the contaminated air for purification is moist. That is,the contaminated air to be cleaned may have a certain relative humiditysuch that sufficient water is present on the surfaces of thephotoactivated semiconductor photocatalyst (e.g., condensed on thephotocatalyst). In some instances, the water from humid air condensed onthe photoactivated semiconductor photocatalyst and may or may not bevisible to the naked eye, but is present in sufficient quantity to formreductive and/or oxidative reactive species.

For purification of dry contaminated air, where there is insufficienthumidity in the contaminated air to provide water to the photocatalyticsystems 140 a/140 b, water or humidity may be brought into the airpurifier. As mentioned, humidity sensors within the air purifier cancollect humidity data, send the data to a microprocessor, and themicroprocessor may control a secondary device to add moisture to theinlet air or to the photocatalytic system. For example, air purifier 100in FIG. 1 may further comprise a water or water vapor inlet, and wherenecessary, a water or water vapor outlet (these optional features arenot illustrated). The water inlet to the air purifier 100 may beconfigured to feed water to a built-in humidifier configured inside theair purifier 100. In various embodiments, water vapor from the built-inhumidifier may be injected directly into the air stream flowing throughthe air inlet tube 122, wherein the moisture is then carried along withthe contaminated air to the photocatalytic systems 140 a and 140 b. Thetemperature of the catalyst surfaces within the photocatalytic systems140 a and 140 b may also be lowered to temperatures below the dew pointof the intake air, promoting water condensation on the catalystsurfaces. In other embodiments, water may be atomized into the airintake tube 122 through an atomizing nozzle under pressure or by way ofan ultrasonic nebulizer, and these fine particulates are carried to thephotocatalytic surfaces by the movement of the air.

1. PCB Card Stack Photocatalytic System

In various embodiments, an air purifier and methods of air purificationcomprise at least one photocatalytic system (FIG. 1, 140 a/140 b) thatfurther comprises a PCB card stack. A PCB card stack refers herein to aplurality of printed circuit boards (PCBs) configured in athree-dimensional array, wherein each PCB is coated with aphotoactivated semiconductor photocatalyst. In various embodiments, thestacking of spaced apart and parallel arranged PCB cards (i.e., face toface) creates a particular airflow pathway through the photocatalyticsystem, such as a serpentine pathway.

Various embodiments of a PCB card stack 200 is illustrated in FIG. 2,noting that in FIG. 1, a dashed circle indicates that FIG. 2 is anenlarged view of one of the photocatalytic systems 140 a that featuresthe stacked PCB card configuration.

In FIG. 2, a PCB card stack is shown fashioned as a photoreactorcontained in a housing 210. The housing 210 may be nothing more than anopen frame so that the light emitted from the incident radiation source(lamp) can still impinge on the photocatalysts present as layers in thephotocatalytic system 200 without the structure blocking the light. Inother embodiments, the housing 210 can be quartz glass or other suitablestructure transparent to the incident radiation. The housing 210 is alsoused to ensure air flows properly through the photocatalytic system 200so as to make contact with layers of photoactivated semiconductorphotocatalyst.

As illustrated in FIG. 2, the PCB card stack photocatalytic system 200further comprises an air inlet 202 through which contaminated air 203enters, and an air outlet 204 out which purified air 205 exits. Withreference to FIG. 1, the air channels 124 a/124 b can be directed intothe air inlet 202 of PCB card stack 200, and the air outlet channels 126a/126 b can be connected to the air outlet 204 of PCB card stack 200. Asdiscussed previously, the number of air channels may depend on thenumber of photocatalytic systems 200 employed in the air purifier.

The contaminated air 203 entering the photocatalytic system 200comprises one or more airborne contaminants 206, such as one or morespecies of airborne microorganism.

As illustrated in FIG. 2, the PCB card stack photocatalytic system 200comprises a plurality of coated PCB cards 220, spaced apart to provide aseries of air channels 221. Although in FIG. 2 only ten PCB cards 220are shown in the PCB card stack photocatalytic system 200, theillustrated example should not be interpreted as being limited. Thenumber of PCB cards in a PCB card stack may be quite large, such asdozens up to hundreds of PCB cards or more. As shown, the individual PCBcards are spaced apart and stacked in a parallel configuration, but in aslightly staggered arrangement so that air flow (indicated by the dasheddirectional arrows) follows a serpentine pathway through the system 200,necessarily passing across each coated PCB card as the air is conveyedthrough each channel 221 configured between the cards in the array.Stated another way, the serpentine airpath ensures the contaminated airpasses over each PCB card in series through the stack.

With continued reference to FIG. 2, each coated PCB card 220 furthercomprises an electrical connector 230, each connector further comprisingan electronic interface 231 connecting to electronic components on thePCB card, along with (+) and (−) leads. This illustration should by nomeans be interpreted as limiting. For example, the (+) and (−)electrodes may be on opposing edges of a PCB card rather than togetheron the same edge. In other embodiments, each card only receives a (+) ora (−) pole, and the opposite polarity connection might be to an elementconfigured outside of the photocatalytic system 200. Or, cards mightalternate as positively charged or negatively charged. In theillustration, each PCB card is polarized by applying a (+/−) potentialon each card such that each card is bipolar.

In various embodiments, each of the (+) leads from all the PCB cards areganged together and each of the (−) leads from all the PCB cards areganged together. In various embodiments, each card is plugged into anelectrified frame such that plugging the cards into the frame acts togang each of the (+) and each of the (−) leads together, making thesystem more modular.

The electrical connectors 230 allow a potential to be applied to eachPCB card so as to polarize each PCB card, i.e., make the card bipolar,which is explained below in reference to FIG. 3. In various embodiments,PCB cards 220 can be pulled out from the housing 210 to be cleaned,recoated with photocatalyst, or replaced, as necessary.

In various embodiments, the air flow through the PCB card stackphotocatalytic system 200 depends on a number of variables, includingthe input air pressure (controlled to some extent by the intake fan 120in FIG. 1 to push air through, and an optional output fan, not shown, topull air through), the number of PCB cards 220 in the stack dictatingthe number of air channels 221, and the size of the individual airchannels 221, which is determined in part by the spacing between PCBcards 220.

In various embodiments, a photocatalytic system comprising a PCB cardstack configuration, such as illustrated in FIG. 2, may comprise an airinlet 202 and an air outlet 204 each measuring about 90 mm (3.5inches)×5 mm (0.2 inches). In various embodiments, such a photocatalyticsystem may measure about 117 mm (4.6 inches) in height, 135 mm (5.3inches) in length, and 95 mm (3.7 inches) in width. These exemplarydimensions are not intended to be limiting in any way.

In various embodiments, the photocatalytic system 200 further comprisesat least one ionizer 270 configured in an airflow channel prior to theinlet of the photocatalytic system 200. The ionizer 270 is configured tocharge the various airborne pollutants 206 entering the system. Invarious embodiments, the ionizer 270 further comprises ESD needles 272that discharge electrons (e−) that are picked up by the pollutants 206,thus becoming charged particles 208. The charged pollutant particlesthen enter the stack of cards where they encounter charged PCB cards. Inparticular, and as perhaps best seen in FIG. 3, each photoactivatedsemiconductor photocatalyst layer disposed on each PCB card ispolarized, and thus the charged pollutant particles 208 are attractedspecifically to the polarized photocatalyst layer, ensuring a residencetime for the particle on the photocatalyst to react with the reductiveand/or oxidative reactants present thereon. This aspect is particularlyimportant for deactivating airborne virus particles, wherein the chargedviral particles can attach to the polarized photocatalyst layer for asufficient time for the biomolecules, such as RNA, to be denatured bythe various reactive species present on the photocatalyst surface.

FIG. 3 depicts a single exemplary PCB card 300, which in variousembodiments, can be equivalent to one of the PCB cards 220 used in thephotocatalytic system 200 illustrated in FIG. 2. An individual coatedPCB card 300 comprises a PCB board 310 and a number of layers disposedon the PCB, each layer applied for example by a deposition process.

In FIG. 3, the PCB card 300 comprises a layer of photoactivatedsemiconductor photocatalyst 340 attached to the underlying substrate 320via a cured adhesive 330. The board may further comprise two electrodesusable for connecting the PCB to a voltage source and polarizing thephotoactivated semiconductor photocatalyst layer 340. In variousembodiments, a positive electrode 352 and a negative electrode 354 areconfigured on the PCB such that the adhesive layer 330 and thephotocatalyst layer 340 are overtop of the two electrodes. The twoelectrodes may be in any dimensional configuration, with theillustration showing the electrodes as thin conductive strips disposedparallel to one another on opposite ends of the PCB card.

In various embodiments, structural tabs 312 and 314 are configured onthe PCB, such as in opposite corners, opposing edges, or even on thesame edge. The tabs may be used to attach each PCB to an electrifiedframe, such as by plugging the tab into a corresponding slot configuredin the frame. Each tab may further comprise the electrical contact,namely the positive contact 350 a that connects to the positiveelectrode 352, and the negative contact 350 b that connects to thenegative electrode 354. The metal electrodes 352 and 354 may bedeposited first on the substrate 320 by various lithographic methods,including a mask layer to mark off where the metal deposits are to go.In other embodiments, a PCB may begin with a uniform conducting layer,such as copper and the conducting layer masked off and then etched toleave behind the two electrode strips. In various embodiments, thesubstrate 320 of the PCB comprises Si, optionally with a SiO₂ layer. Theelectrodes 352/354 may comprise Pt, Pd, Ru, Ag, Ag, Cu, and so forth.

The base PCB 310 may comprise a simple layer single sided MCPCB with ametal base (Al, Cu, or Cu alloy), a dielectric layer, a copper circuitlayer, IC components and a solder mask. In various embodiments, achip-on-board COB MCPCB may be used. Such PCBs for use herein areavailable, for example, from Shenzhen JDB Technology Co., Ltd.,Hangzhou, China.

To prepare a working PCB card for use in a PCB card stack, aphotocatalyst layer is disposed on the PCB card that already includesthe electrode strips (deposited thereon or formed by etching away thecircuit layer everywhere except for the electrodes). As discussed hereinabove, many methods may be used to dispose a photocatalyst layer on aPCB card, such as via an adhesive disposed over the electrodes and theunderlying substrate. An adhesive coated PCB may be exposed, forexample, to a fog comprising water, surfactant, and photoactivatedsemiconductor photocatalyst mixture. The mixture rapidly condenses tocreate airborne photocatalyst impregnated water droplets that surroundand embed into the adhesive layer 330 on the board 310. The resultingPCB card is then exposed to a curing process that hardens the adhesiveto permanently capture and hold the photocatalyst layer 340 in place onthe PCB card. In various embodiments, the photoactivated semiconductorphotocatalyst in the fog comprises nanoparticles, with thenanoparticulate structure remaining in the finished photocatalytic layer340. As mentioned and discussed above, many other methods may be used toform a layer of photocatalyst on a PCB card.

Each of the PCB cards 300 are then stacked in a frame by alternatingattachment of an edge or two edges of each card to either a left frameor a right frame, so as to create the serpentine air flow path as perFIG. 2, and to electrify each board so that each photoactivatedsemiconductor photocatalytic layer is polarized. The two opposite sidesof the frame can include a bus so that by plugging in an individual PCBcard into the frame, the electrodes are connected up to the common line.

In practice, resistors at each board connection can be used so that thepotential applied to each PCB card in the stack is different. In variousembodiments, the potential may be lower or higher for each cardsequentially through the stack in the direction of the airflow asneeded. In various embodiments, certain PCB cards may have differentpotentials such that there is no cognizable gradient of potentialsthrough the photocatalytic system of stacked PCB cards.

As illustrated in FIG. 2, pollutant particles 208, having been chargedby the ionizer 270, will be attracted to the polarized PCB cards havingthe photoactivated semiconductor photocatalyst layers (340 in FIG. 3).This attraction (e.g., a negatively charged airborne pollutant attractedto the (+) side of a PCB card) results in a residence time for theparticle on the catalyst layer sufficient for the reactive speciespresent thereon to denature biomolecules in the particle, or otherwisedestroy odoriferous molecules, and so forth. As mentioned, in practice,the PCB card is polarized by applying a potential to the card, but whencharged particles attract to the polarized PCB card, the particlesnecessarily run into the photocatalytic layer disposed on the PCB card.

2. Photocatalytic System Comprising 3-DOM Structure or OtherThree-Dimensional Architecture

In various embodiments, a photocatalytic system for use herein comprisesa photoactivated semiconductor photocatalyst in a 3-DOM structure, suchas an inverse opal. Stated another way, a preferred photocatalyticsystem comprises an inverse opal photoactivated semiconductorphotocatalyst. Preparation of 3-DOM lattices was discussed herein above.

In various embodiments, the 3-DOM lattice may be 3D printed and thendip-coated and air blasted with the one or more photocatalysts such thatthe photoactivated semiconductor catalyst is sieved into and through the3-DOM structure. The end result is a photoactivated semiconductorphotocatalyst having a 3-dimensional structure.

FIG. 4 illustrates an exemplary photocatalytic system 400 comprising aphotoactivated semiconductor photocatalyst with a 3-DOM structure. The3-DOM structure herein is essentially an open cell structure comprisingholes 410 measuring from about 1 mm to about 5 mm in average diameter.The open cell structure provides pathways for air 412 to circulatethrough. In various embodiments, the lattice 420 itself may comprise asemiconductor photocatalytic material. In various embodiments, thelattice 420 may comprise a single semiconductor photocatalyst embeddedin a resin matrix, or an intimate mixture of more than one semiconductorphotocatalyst. In other embodiments, the lattice 420 comprises only onecomponents of a two-component photoactivated semiconductor system, andthe other component in the photoactivated semiconductor photocatalystsystem appears as particles 430 (e.g., nanoparticles, crystals, oramorphous particle) within the architecture, such as adhered to latticesurfaces. In still further embodiments, the lattice 420 may compriseonly a lattice material having no photocatalytic properties, like aresin, and the particles 430 comprise the one or more semiconductorphotocatalysts present in the photoactivated semiconductorphotocatalytic system.

3. Photocatalytic System Comprising a Combination of PCB Card Stack and3-DOM Structure

In various embodiments, a photocatalytic system for use herein comprisesboth a PCB card stack as discussed above in Part 1 and a 3-DOM structurein combination. In various embodiments, the 3-DOM lattice structurecreates “tripping turbulence” for the contaminated air entering the PCBcard stack.

In various embodiments, the 3-DOM lattice trips turbulence by actinglike a filter prior to entering the PCB card stack. Although thediameter of the holes in the 3-DOM lattice may vary (e.g., from 1 mm toabout 5 mm), the 3-DOM lattice can be positioned such that it directslight in a particular direction. In various embodiments, ESD needles ofan ionizer may be used to create turbulence in addition to charging theparticulate pollutants prior to entering the PCB card stack.

II. Methods of Air Purifier—General Aspects

In various embodiments, the present disclosure includes methods of airpurification. In various embodiments, methods of air purificationutilize an air purifier in accordance with the present disclosure. Themethods also provide air decontamination, air deodorization, aircleaning, air filtering, and air sanitizing, depending on the nature ofthe contaminants present in the air requiring purification.

The method generally comprises placing contaminated air into contactwith a photoactivated semiconductor photocatalyst irradiated withincident radiation configured to excite the photoactivated semiconductorphotocatalyst. The photoactivated semiconductor photocatalyst may bepart of a photocatalytic system comprising additional features that mayphysically support the photoactivated semiconductor photocatalyst ormake it more efficient, such as by increasing the probability thecontaminated air, and the airborne contaminants therein, contact thephotoactivated semiconductor photocatalyst.

In various embodiments, a method of air purification comprises placingcontaminants present in the air into contact with a surface of aphotoactivated semiconductor photocatalyst irradiated with incidentradiation configured to excite the at least one component therein andgenerate reductive and/or oxidative reactive species from at least oneof oxygen or water to destroy or deactivate the contaminants. In variousembodiments, reactive species generated on the photoactivatedsemiconductor photocatalyst comprise at least one of hydrogen peroxide(H₂O₂), hydroperoxyl radical (HO₂.), hydroxide anion (HO⁻), hydroperoxylradical anion (HO₂.⁻), hydroxyl radical (HO.), hydronium ion (H₃O+) orsuperoxide radical anion (.O₂ ⁻).

In various embodiments, the airborne contaminants present in the airinclude inanimate pollutants and microorganisms. In various embodiments,the airborne inanimate pollutants include, but are not limited to, dust,smoke, grease, oils, ashes, hair, skin dander, odoriferous moleculessuch as amines and thiols, and pollen. In various embodiments, airbornemicroorganisms include, but are not limited to, airborne bacteria,viruses, molds, yeasts and spores. In various embodiments, contaminatedair comprises both microorganisms and the odors they produce.

In various embodiments, hydrogen peroxide (H₂O₂), hydroperoxyl radical(HO₂.), hydroxide anion (HO⁻), hydroperoxyl radical anion (HO₂.⁻),hydroxyl radical (HO.), hydronium ion (H₃O+) and/or superoxide radicalanion (.O₂ ⁻) generated from oxygen and/or water present on the surfaceof the photoactivated semiconductor photocatalyst are capable ofreducing/oxidizing organic molecules such as amines and thiols toconvert odoriferous substances into odorless molecules. In variousembodiments, organic molecules are reductively or oxidatively cleaved bythe air purification methods herein.

In various embodiments, hydrogen peroxide (H₂O₂), hydroperoxyl radical(HO₂.), hydroxide anion (HO⁻), hydroperoxyl radical anion (HO₂.⁻),hydroxyl radical (HO.), hydronium ion (H₃O+) and/or superoxide radicalanion (.O₂ ⁻) thus generated from oxygen and/or water present on thesurface of the photoactivated semiconductor photocatalyst are capable ofreducing/oxidizing organic molecules and biopolymers such as RNA, DNAand proteins, resulting in the destruction or deactivation of airborneand living bacteria, viruses, molds, yeasts and spores.

In various embodiments, a photoactivated semiconductor photocatalyticused in the methods of air purification herein comprises at least onesemiconductor photocatalyst as defined herein above.

Methods of air purification may be performed by using an air purifier inaccordance with the present disclosure. As discussed herein, an airpurifier in accordance with various embodiments comprises: aphotocatalytic system comprising a photoactivated semiconductorphotocatalyst; and a lamp configured to irradiate the photoactivatedsemiconductor photocatalyst with incident radiation configured to excitethe photoactivated semiconductor photocatalyst, wherein thephotocatalyst system is configured to generate at least one of hydrogenperoxide (H₂O₂), hydroperoxyl radical (HO₂.), hydroxide anion (HO),hydroperoxyl radical anion (HO₂.⁻), hydroxyl radical (HO.), hydroniumion (H₃O+) or superoxide radical anion (.O₂ ⁻) from oxygen and/or waterpresent on the photoactivated semiconductor photocatalyst.

In various embodiments, a method of purifying contaminated air comprisesconveying the contaminated air into an air purifier, the air purifiercomprising (i) a photocatalytic system further comprising aphotoactivated semiconductor photocatalyst and (ii) a lamp configured toirradiate and excite the photoactivated semiconductor photocatalyst withincident radiation, wherein contaminants present in the contaminated aircontact a surface of the photoactivated semiconductor photocatalyst,wherein the photocatalyst system is configured to generate to generateat least one of hydrogen peroxide (H₂O₂), hydroperoxyl radical (HO₂.),hydroxide anion (HO⁻), hydroperoxyl radical anion (HO₂.⁻), hydroxylradical (HO.), hydronium ion (H₃O+) or superoxide radical anion (.O₂ ⁻)from oxygen and/or water present on the photoactivated semiconductorphotocatalyst, destroying, denaturing or deactivating the contaminants.

In various embodiments, a method of purifying contaminated air comprisesdeactivating airborne single-stranded virus particles, includingSARS-CoV-2.

In various embodiments, a method purifying contaminated air furthercomprises positively or negatively charging airborne contaminates sothat the charged contaminates are attracted by electromotive forces tovarious +/− charged features in a photocatalytic system. This attractionensures sufficient contact time between the charged contaminantparticles and the charged features within the photocatalytic system forthe reductive and/or oxidative reactant species in the photocatalyticsystem to reduce, oxidize, deodorize, deactivate and/or destroy theairborne contaminants.

III. Examples

FIG. 5 sets forth the results of a simulation experiment. The simulationused a PCB card stack having eleven (11) PCB cards stacked such that aserpentine airflow path comprised twelve (12) parallel airpath channels.The simulation results highlight the control of turbulence whileminimizing the loss of pressure. This can be interpreted as minimal heatloss, and other geometries may be considered. In the illustration,numbers 1-16 are assigned as a guide for the reader to interpret theshading on the serpentine airflow diagram. The diagram shows bars ofpressure in each of the air channels between the PCB cards in the stack,and at the inlet and outlet.

In the detailed description, references to “various embodiments”, “oneembodiment”, “an embodiment”, “an example embodiment”, etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is submitted that it iswithin the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described. After reading the description, itwill be apparent to one skilled in the relevant art(s) how to implementthe disclosure in alternative embodiments.

Steps recited in any of the method or process descriptions may beexecuted in any order and are not necessarily limited to the orderpresented. Furthermore, any reference to singular includes pluralembodiments, and any reference to more than one component or step mayinclude a singular embodiment or step. Also, any reference to attached,fixed, connected, coupled or the like may include permanent (e.g.,integral), removable, temporary, partial, full, and/or any otherpossible attachment option. Any of the components may be coupled to eachother via friction, snap, sleeves, brackets, clips or other means nowknown in the art or hereinafter developed. Additionally, any referenceto without contact (or similar phrases) may also include reduced contactor minimal contact.

Benefits, other advantages, and solutions to problems have beendescribed with regard to specific embodiments. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure. The scope of the disclosure is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to ‘at least one of A, B, and C’ or ‘atleast one of A, B, or C’ is used in the claims or specification, it isintended that the phrase be interpreted to mean that A alone may bepresent in an embodiment, B alone may be present in an embodiment, Calone may be present in an embodiment, or that any combination of theelements A, B and C may be present in a single embodiment; for example,A and B, A and C, B and C, or A and B and C.

All structural, chemical, and functional equivalents to the elements ofthe above-described various embodiments that are known to those ofordinary skill in the art are expressly incorporated by reference andare intended to be encompassed by the present claims. Moreover, it isnot necessary for an apparatus or component of an apparatus, or methodin using an apparatus to address each and every problem sought to besolved by the present disclosure, for it to be encompassed by thepresent claims. Furthermore, no element, component, or method step inthe present disclosure is intended to be dedicated to the publicregardless of whether the element, component, or method step isexplicitly recited in the claims. No claim element is intended to invoke35 U.S.C. 112(f) unless the element is expressly recited using thephrase “means for.” As used herein, the terms “comprises”, “comprising”,or any other variation thereof, are intended to cover a non-exclusiveinclusion, such that a chemical, chemical composition, process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such chemical, chemical composition, process, method,article, or apparatus.

1. An air purifier comprising: a photocatalytic system comprising atleast one photoactivated semiconductor photocatalyst; and a lampconfigured to irradiate the photoactivated semiconductor photocatalystwith incident radiation configured to excite the photoactivatedsemiconductor photocatalyst, wherein the photocatalyst system isconfigured to generate at least one reductive or oxidative reactivespecies in the presence of at least one of oxygen or water in contactwith the photoactivated semiconductor photocatalyst.
 2. The air purifierof claim 1, wherein the at least one reductive or oxidative reactivespecies comprises at least one of hydrogen peroxide (H₂O₂), hydroperoxylradical (HO₂.), hydroxide anion (HO⁻), hydroperoxyl radical anion(HO₂.⁻), hydroxyl radical (HO.), hydronium ion (H₃O+) and/or superoxideradical anion (.O₂ ⁻).
 3. The air purifier of claim 1, wherein the atleast one photoactivated semiconductor photocatalyst has an energybandgap (E_(g)) of from about 12.4 eV to about 1.24 meV, referenced toNHE.
 4. The air purifier of claim 3, wherein the incident radiation hasan energy (E_(s)), wherein E_(s)≥E_(g) of the at least onephotoactivated semiconductor photocatalyst.
 5. The air purifier of claim1, wherein the photocatalytic system comprises two photoactivatedsemiconductor photocatalyst having overlapping, non-overlapping, oroffset bandgaps, wherein each bandgap is from about 12.4 eV to about1.24 meV, referenced to NHE.
 6. The air purifier of claim 1, wherein theat least one photoactivated semiconductor photocatalyst is modified byat least one of coupling to an electron transport layer (ETL) material,coupling to a hole transport layer (HTL) material, doping, surfacemodification, or any combination thereof.
 7. The air purifier of claim1, wherein the at least one photoactivated semiconductor photocatalystcomprises an elemental material, metal chalcogenide, metal oxide, metaloxyhalide, metal phosphate, metal hydroxide, metal nitride, metalmolybdate, metal vanadate, or metal tungstate, wherein the metal is Ti,C, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd,In, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg or Tl.
 8. The air purifier ofclaim 7, wherein the at least one photoactivated semiconductorphotocatalyst is selected from the group consisting of Bi₂Mo₃O₁₂,Bi₂Mo₂O₉, Bi₂MoO₆, BiVO₄, Bi₂WO₆, BiOBr, BiOI, MoS₂, CuO, Cu₂O, MoO₃,WO₃, BiPO₄, Ag₃PO₄, TiO₂, SnO₂, InVO₄, FeVO₄, Ag₄V₂O₇, Fe₃O₄, andmixtures thereof.
 9. The air purifier of claim 1, wherein thephotocatalytic system comprises two photoactivated semiconductorphotocatalysts consisting of Bi₂MoO₆ and Ag₃PO₄.
 10. The air purifier ofclaim 1, wherein the lamp comprises a low pressure mercury vapor lampconfigured to radiate UV-C incident electromagnetic radiation at awavelength of about 254 nm.
 11. The air purifier of claim 1, wherein thephotocatalytic system further comprises a stack of PCB cards, each PBCcard comprising a layer of the at least one photoactivated semiconductorphotocatalyst disposed thereon, the photocatalytic system comprising aplurality of PCB cards stacked in a parallel and staggered arrangementcreating a serpentine airflow pathway.
 12. The air purifier of claim 11,wherein each PCB card in the stack of PCB cards is bipolarized with anapplied electrical potential.
 13. The air purifier of claim 1, furthercomprising an ionizer configured to negatively or positively chargeairborne contaminants in an air pathway leading into the photocatalyticsystem.
 14. The air purifier of claim 1, wherein the photocatalyticsystem comprises a photoactivated semiconductor photocatalyst having a3-DOM structure.
 15. The air purifier of claim 14, wherein the 3-DOMstructure comprises a 3-dimensional lattice resin having an open cellstructure with holes of from about 1 mm to about 5 mm in averagediameter, and wherein the at least one photoactivated semiconductorphotocatalyst is present in the resin or on the resin.
 16. The airpurifier of claim 14, wherein the 3-DOM structure comprises a 3D printed3-dimensional lattice.
 17. The air purifier of claim 1, furthercomprising a humidifier configured to inject water vapor into an airpathway leading into the photocatalytic system.
 18. The air purifier ofclaim 1, further comprising an intake fan configured to pullcontaminated air into the air purifier and move the air through thephotocatalytic system.
 19. The air purifier of claim 1, furthercomprising an ozone trap configured to remove ozone generated from thephotocatalytic system, the lamp or the combination thereof.
 20. A methodof destroying or deactivating airborne contaminants present incontaminated air, the method comprising: contacting the contaminantspresent in the contaminated air with a surface of a photoactivatedsemiconductor photocatalyst irradiated with incident radiationconfigured to excite the photoactivated semiconductor, whereinirradiation of the photoactivated semiconductor photocatalyst generatesreductive and/or oxidative reactive species from at least one of oxygenor water present on the surface of the photoactivated semiconductorphotocatalyst, and wherein the reductive and/or oxidative reactivespecies thus generated destroy or deactivate the airborne contaminants.21. The method of claim 20, wherein the reductive and/or oxidativereactive species generated comprise at least one of hydrogen peroxide(H₂O₂), hydroperoxyl radical (HO₂.), hydroxide anion (HO⁻), hydroperoxylradical anion (HO₂.⁻), hydroxyl radical (HO.), hydronium ion (H₃O+) orsuperoxide radical anion (.O₂ ⁻).
 22. The method of claim 20, whereinthe at least one photoactivated semiconductor photocatalyst has anenergy bandgap (E_(g)) of from about 12.4 eV to about 1.24 meV,referenced to NHE.
 23. The method of claim 22, wherein irradiation ofthe photoactivated semiconductor photocatalyst further comprisesirradiation with incident radiation of having an energy (E_(s)) greaterthan or equal to a bandgap energy (E_(g)) of the at least onephotoactivated semiconductor photocatalyst.
 24. The method of claim 20,wherein contacting the contaminants present in the contaminated air witha surface of a photoactivated semiconductor photocatalyst furthercomprises conveying the contaminated air through a serpentine airflowpathway configured between a plurality of spaced apart PCB cards stackedin a parallel arrangement, wherein each PCB card comprises a layer ofthe at least one photoactivated semiconductor photocatalyst.
 25. Themethod of claim 24, further comprising positively or negatively chargingthe contaminants in the contaminated air prior to the contaminantscoming into contact with a surface of the photoactivated semiconductorphotocatalyst.
 26. The method of claim 25, further comprising applyingan electrical potential to each of the PCB cards such that anelectric/electromagnetic field produced around each PCB card attractscharged contaminants to the layer of the at least one photoactivatedsemiconductor photocatalyst.
 27. The method of claim 20, whereindestroying or deactivating the contaminants further comprises destroyingor deactivating an airborne microorganism.
 28. The method of claim 20,wherein destroying or deactivating the contaminants further comprisesdeactivating an airborne single-stranded RNA virus particle.
 29. Themethod of claim 28, wherein the deactivating of the airbornesingle-stranded RNA virus particle further comprises contacting theairborne single-stranded RNA virus particle with a surface of thephotoactivated semiconductor photocatalyst for a time sufficient for thereductive and/or oxidative reactive species thus generated to denature abiomolecule present in the single-stranded RNA virus particle.
 30. Themethod of claim 20, wherein the contaminates include airborne SARS-CoV-2virus particles.